In industry there is an ever increasing need for pipes protected from the corrosive action of the various materials conveyed by way of pipelines.
Experience has shown that the most lasting and reliable protection is given to underground pipelines by a coating of vitreous enamels of various compositions, which are by far more durable than coatings of heated bitumen and various kinds of organic varnish and film.
To meet the stringent requirements concerning the quality of enamel coatings, such as 100 percent continuity, uniform thickness of the enamel coating, and freedom from other defects adversely affecting anticorrosion protection, it is necessary to provide equipment capable of perfectly performing the various enameling operations.
One of the enameling operations in question is application of enamel slip to the surfaces of the pipes to be enameled.
In the present art, no apparatus for applying enamel slip to a pipe surface can give the required quality of slip application, nor can they effect simultaneous application of slip to the external and internal surfaces of pipes (see, for example, U.S.S.R. Inventor's Certificate No. 204089, Int. Cl. C23d 5/00, 1965).
Known in the art is an apparatus for applying enamel slip to the internal and external surfaces of a pipe, comprising enamel slip reservoirs, a frame, and movable and stationary vises. The frame is rotatable about a horizontal axis and mounts lengthwise lead screws carrying a carriage with a ball-jointed vise. The apparatus further comprises a vertical column-type screw with a sliding nut whereon is rotatably mounted a reciprocating incomplete ring with sprayers and tracing rollers.
This apparatus suffers from the disadvantage that the tracing rollers thereof are in constant mechanical contact with the external surface of the pipe, causing damage to the coating. Another disadvantage is that the internal and external surfaces of the pipe cannot be coated simultaneously and that consumption of enamel slip is substantially large.
Also known in the art is a pipe enameling apparatus comprising an enamel slip applying device (U.S.S.R. Inventor's Certificate No. 129448, Cl. C23d 5/00, 1959). It suffers from the disadvantage that enamel slip can be applied only to the internal surface of the pipe and, furthermore, the vessel by means of which slip is fed inside the pipe dies not provide constant slip circulation, which adversely affects the adhesive properties of the slip and, consequently, the quality of the coating applied.
Also known in the art is an apparatus for applying enamel slip to the external surface of a pipe, which apparatus is constructed as a vessel filled with enamel slip and has a bottom with a seal-equipped hole through which the pipe under treatment is moved.
This apparatus suffers from the disadvantage that it applies enamel slip only to the external surface of the pipe. Another disadvantage is that there is mechanical contact between the pipe surface and the seal, which adversely affects the continuity of the coating and impairs its quality. Still another disadvantage of the apparatus under consideration is that the slip in the vessel is not agitated during the application process, which leads to separation of its colloidal structure and degradation of adhesive properties. Lastly, the apparatus does not maintain constant slip temperature, which adversely affects the physicomechanical properties of the enamel slip.
It is an object of the present invention to provide for enhancing the quality of pipe enamel coatings.
It is a further object of the present invention to solve the problem of applying enamel coatings simultaneously to the external and internal surfaces of a pipe.
It is a still further object of the present invention to decrease the amount of enamel slip consumed in the process of pipe enameling.
It is a still further object of the present invention to prolong pipe service life.